cassandra-user mailing list archives

Hi all,
I have a rather strange problem I'd like to address. As I understand it a
write in cassandra always overwrites already existing data, so it is not
possible to have a way to create an index pointing to the first entry
matching some criteria. What I mean is that I have a CF which stores user
purchases and now I want to find the first time a user bought an item from a
certain class of objects. For this I was thinking about a CF with SCFs, the
CF key being the user ID and the SCF key being the class id of the item and
then the value would be the key of the purchase in the purchases CF.
Obviously for this to work I'd have to check if a value like
firstPurchases[123][987] already exists and if not write it, but it there a
way to implement it without the additional read?
Regards,
Chris